ChemGlobe: Ytterbium
   Electronic, thermal, and steric data along with an isotope table.
   http://partisans.spurious.biz/~pkremer/projects/chemglobe/ptoe/_/70.html

ChemicalElements.com: Ytterbium
   Basic information, atomic structure, and isotopes.
   http://www.chemicalelements.com/elements/yb.html

EnvironmentalChemistry.com: Ytterbium
   Atomic structure, chemical and physical properties, and table of nuclides.
   http://environmentalchemistry.com/yogi/periodic/Yb.html

It's Elemental: Ytterbium
   Basic physical and historical information.
   http://education.jlab.org/itselemental/ele070.html

LANL: Ytterbium
   History, sources, properties, and uses.
   http://periodic.lanl.gov/elements/70.html

Lenntech: Ytterbium
   Physical data, chemical properties, health and environmental effects.
   http://www.lenntech.com/Periodic-chart-elements/Yb-en.htm

Visual Elements: Ytterbium
   Image, physical information, and ionisation energies.
   http://www.chemsoc.org/viselements/pages/ytterbium.html

Wikipedia: Ytterbium
   Properties of the element, including its history, applications, and characteristics.
   http://en.wikipedia.org/wiki/Ytterbium